Capacity Control Valve, Variable Capacity Compressor and Capacity Control System Therefor

ABSTRACT

Provided are a capacity control valve, a variable capacity compressor, and a capacity control system, which control a discharge capacity stably even when a cooling load is small, and reduce the risk of damaging a compressor even in a state when the quantity of a refrigerant is insufficient. The capacity control valve ( 300 ) for the variable capacity compressor includes a solenoid unit ( 300 B), a valve body ( 306 ) on which the pressure of a discharge chamber ( 142 ) of the variable capacity compressor acts in a valve opening direction, and the pressure of a suction pressure area of the variable capacity compressor and the electromagnetic force of the solenoid unit ( 300 B) act in a valve closing direction opposite to the valve opening direction, and a pressure sensitive unit ( 340 ) on which the pressure of the discharge chamber ( 142 ) acts, and which is connected to the valve body ( 306 ) to apply urging force in the valve opening direction on the valve body ( 306 ) according to the pressure of the discharge chamber ( 142 ) when the pressure of the discharge chamber ( 142 ) is lower than a set pressure, and is separated from the valve body ( 306 ) when the pressure of the discharge chamber ( 142 ) is higher than the set pressure.

TECHNICAL FIELD

The present invention relates to a capacity control valve, a variable capacity compressor, and a capacity control system for the variable capacity compressor, and, particularly, to a capacity control valve and a variable capacity compressor suitable for a vehicular air conditioning system, and a capacity control system for the variable capacity compressor.

BACKGROUND ART

A variable capacity reciprocating compressor used in an vehicular air conditioning system, for example, has a housing in which a discharge chamber, a crank chamber, a suction chamber, and cylinder bores are defined. Pistons are placed in the cylinder bores, and a drive shaft is rotatably supported in the housing.

The drive shaft rotates with the engine as a power source, and a conversion mechanism converts rotation of the drive shaft into reciprocating motion of the pistons. According to the reciprocating motion of the piston, suction of an operating fluid from the suction chamber into the cylinder bore, compression of the sucked operating fluid and discharge of the compressed operating fluid to the discharge chamber are carried out in order.

In the reciprocating variable capacity compressor, the stroke length of the piston, i.e., the discharge capacity of the compressor is varied by varying the pressure (control pressure) in the crank chamber (control pressure chamber). A capacity control valve to control the discharge capacity is disposed in a supply passage communicating the discharge chamber with the crank chamber. A throttled portion is formed in an extraction passage communicating the crank chamber with the suction chamber.

The capacity control valve is controlled by a control device which performs feedback control on the discharge capacity in a differential pressure control method which causes a pressure difference (differential pressure) between pressure in the discharge chamber (discharge pressure) and pressure in the suction chamber (suction pressure) to approach a target value (see, for example, Patent Literature 1).

Patent Literature 1: Japanese Patent Application Laid-open No. 2001-132650 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the variable capacity compressor, when the cooling load is small, the differential pressure as the control target is set small. As the differential pressure is made smaller, however, the amount of the operating fluid (discharge gas) in the discharge chamber supplied to the crank chamber decreases, so that there are cases where the discharge capacity cannot be controlled stably. As a result, the drive torque of the variable capacity compressor varies, which may adversely affect the control on the engine speed. In addition, the discharge capacity may not become smaller than is intended, so that the suction pressure drops to freeze the evaporator.

Suppose that the amount of a refrigerant filled in the refrigeration circuit, for example, is deficient. In this assumed case, the differential pressure drops more than that in the case where the filled amount is proper. According to the differential pressure control method, when the differential pressure tends to drop, the control device increases the discharge capacity to keep the differential pressure at a predetermined value.

According to the differential pressure control method, the discharge capacity is increased until the differential pressure reaches the target value. When the filled amount of the refrigerant is short and the amount of circulation thereof is short, however, the differential pressure does not reach the target value, and the discharge capacity is increased in an accelerated manner to finally reach the maximum capacity. In the assumed case, the differential pressure control method has the disadvantage that damage of the compressor is accelerated.

It is an object of the invention to provide a capacity control valve, a variable capacity compressor, and a capacity control system, which control a discharge capacity stably even when a cooling load is small, and reduce a risk of damaging a compressor even in a state when the quantity of a refrigerant is insufficient.

Means for Solving the Problems

To overcome the aforementioned problems, according to one mode of the invention, there is provided a capacity control valve, disposed in a communication passage communicating a discharge pressure area with a control pressure chamber in a variable capacity compressor, for regulating a pressure in the control pressure chamber to control a discharge capacity of the variable capacity compressor, the capacity control valve comprising a solenoid unit; a valve body on which a pressure of the discharge pressure area of the variable capacity compressor acts in a valve opening direction, and a pressure of a suction pressure area of the variable capacity compressor and an electromagnetic force of the solenoid unit acts in a valve closing direction opposite to the valve opening direction; and a pressure sensitive unit on which the pressure of the discharge chamber acts, and which is connected to the valve body to apply urging force in the valve opening direction on the valve body according to the pressure of the discharge pressure area when the pressure of the discharge pressure area is lower than a set pressure, and is separated from the valve body when the pressure of the discharge pressure area is higher than the set pressure (claim 1).

In a preferable mode, a first pressure receiving area of the valve body on which the pressure of the discharge pressure area acts is equal to or greater than a second pressure receiving area of the valve body on which the pressure of the suction pressure area of the variable capacity compressor acts (claim 2).

In a preferable mode, the pressure sensitive unit is disposed in such a way that the pressure of the discharge pressure area acts on the pressure sensitive unit and the valve body in opposite directions (claim 3).

In a preferable mode, the first pressure receiving area is set, in the pressure sensitive unit, substantially identical to a third pressure receiving area on which the pressure of the discharge pressure area acts (claim 4).

In a preferable mode, the pressure sensitive unit is disposed, in the communication passage, in an area extending between the discharge pressure area and a valve hole of the capacity control valve (claim 5).

According to another mode of the invention, there is provided a variable capacity compressor comprising a housing having a discharge chamber as the discharge pressure area, a crank chamber as the control pressure chamber, a suction chamber, and a cylinder bore defined therein; a piston placed in the cylinder bore; a drive shaft rotatably supported in the housing; a conversion mechanism including a swash plate element of a variable tilt angle which converts rotation of the drive shaft to a reciprocal motion of the piston; and any one of the aforementioned capacity control valves (claim 6).

According to another mode of the invention, there is provided a capacity control system for a variable capacity compressor, comprising any one of the aforementioned capacity control valves, external information detecting means which detects external information, control target setting means which sets a control target value based on the external information detected by the external information detecting means, and current regulating means which regulates a current to be supplied to the solenoid unit based on the control target value set by the control target setting means, and controlling a discharge capacity of the variable capacity compressor by regulating the pressure of the control pressure chamber, the external information detecting means including discharge pressure detecting means for detecting the pressure of the discharge pressure area, wherein when the pressure of the discharge pressure area detected by the discharge pressure detecting means is lower than the set pressure, the control target setting means sets a target suction pressure which is a target value of the pressure of the suction pressure area as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit based on the target suction pressure (claim 7).

In a preferable mode, when the pressure of the discharge pressure area detected by the discharge pressure detecting means is higher than the set pressure, the control target setting means sets the target suction pressure which is the target value of the pressure of the suction pressure area as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit based on the pressure of the discharge pressure area detected by the discharge pressure detecting means, and the target suction pressure (claim 8).

In a preferable mode, when the pressure of the discharge pressure area detected by the discharge pressure detecting means is higher than the set pressure, the control target setting means sets a target value for the current to be supplied to the solenoid unit as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit in such a way as to approach the target value of the current (claim 9).

Effect of the Invention

When the capacity control valve of claim 1 of the invention is adapted to the variable capacity compressor, in the control range where the pressure in the discharge pressure area is lower than the set pressure, the discharge capacity can be controlled by the suction pressure control method which permits the pressure in the suction pressure area to approach the target instead of the differential pressure control method. Accordingly, even when the cooling load is small, the discharge capacity can be controlled stably, and the risk of damaging the compressor is reduced even when the amount of the refrigerant is insufficient.

According to the capacity control valve of claim 2, excessive releasing operation of the valve body is restrained, so that the opening/closing operation of the valve body becomes stable.

According to the capacity control valve of claim 3, the influence of the pressure in the discharge pressure area which acts on the valve body is reduced, thus improving the accuracy in controlling the suction pressure.

According to the capacity control valve of claim 4, the influence of the pressure in the discharge pressure area which acts on the valve body is substantially eliminated, further improving the accuracy in the suction pressure control.

The capacity control valve of claim 5 has a simple structure.

According to the capacity control valve of claim 6, the minimum piston stroke is defined by the minimum inclination angle of the swash plate. In this type of compressor, the piston stroke can be set very small, so that the minimum discharge capacity is made smaller, widening the control range for the discharge capacity. According to the invention, capacity control is executed stably even with the minimum discharge capacity, so that a wide control range is used effectively.

According to the capacity control system for a variable capacity compressor of claim 7 of the invention, in the control range where the pressure in the discharge pressure area is lower than the set pressure, the discharge capacity is controlled by the suction pressure control method which permits the pressure in the suction pressure area to approach the target instead of the differential pressure control method. Accordingly, even when the cooling load is small, the discharge capacity can be controlled stably, and the risk of damaging the compressor is reduced even when the amount of the refrigerant is insufficient.

According to the capacity control system for a variable capacity compressor of claim 8, even in the control range where the pressure in the discharge pressure area is higher than the set pressure, the discharge capacity is controlled by the suction pressure control method which permits the pressure in the suction pressure area to approach the target. That is, the discharge capacity is controlled by the suction pressure control method regardless of whether the pressure in the discharge pressure area is high or low. When this capacity control system is applied to the refrigeration cycle of an air-conditioning system, the pressure in the discharge pressure area has a strong correlation with the temperature of the evaporator, so that the accuracy of controlling the room temperature by the air-conditioning system is improved.

According to the capacity control system for a variable capacity compressor of claim 9, when in the control range where the pressure in the discharge pressure area is higher than the set pressure, the discharge capacity is controlled by the differential pressure control method. According to the differential pressure control method, it is easy to estimate the torque of the compressor, so that in the region where the pressure in the discharge pressure area is comparatively high (intermediate and high load region), the control of the torque of the compressor can be executed stably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the schematic configuration of the refrigeration cycle of a vehicular air-conditioning system to which a capacity control system according to a first embodiment is applied, together with the vertical cross section of a variable capacity compressor.

FIG. 2 is a diagram for describing how a capacity control valve in the compressor of FIG. 1 is connected.

FIG. 3 is a diagram showing in enlargement a region III in FIG. 2.

FIG. 4 is a cross-sectional view showing in enlargement a pressure sensitive unit in the capacity control valve and the vicinity thereof in FIG. 2 with the pressure sensitive unit abutting on the distal end of the transmission rod.

FIG. 5 is a cross-sectional view showing in enlargement the pressure sensitive unit in the capacity control valve and the vicinity thereof in FIG. 2 with the pressure sensitive unit and the distal end of the transmission rod separated from each other.

FIG. 6 is a graph showing the relationship between a control current I and a Pd−Ps differential pressure in the capacity control system in FIG. 1 with the valve body and the pressure sensitive unit separated from each other.

FIG. 7 is a graph showing the relationship between the control current I and a suction pressure Ps in the capacity control system in FIG. 1 with the valve body and the pressure sensitive unit connected to each other.

FIG. 8 is a block diagram showing the schematic configuration of the capacity control system in FIG. 1.

FIG. 9 is a block diagram for describing the schematic configuration of current regulating means in the capacity control system in FIG. 8.

FIG. 10 is a graph showing the relationship between the control current I, the discharge pressure Pd and the suction pressure Ps when the valve body and the pressure sensitive unit in a capacity control system according to a modification is separated from each other.

DESCRIPTION OF REFERENCE NUMERALS

-   140 Suction chamber (suction pressure area) -   142 Discharge chamber (discharge pressure area) -   300B Solenoid unit -   306 Valve body -   340 Pressure sensitive unit

BEST MODE OF CARRYING OUT THE INVENTION

A capacity control system A for a variable capacity compressor according to an embodiment of the invention will be described below.

FIG. 1 shows a refrigeration cycle 10 of a vehicular air-conditioning system to which the capacity control system A is applied. The refrigeration cycle 10 includes a circulation line 12 along which a refrigerant as an operating fluid circulates. In the circulation line 12, a compressor 100, a radiator (condenser) 14, an expansion device (expansion valve) 16 and an evaporator 18 are interposed serially along the direction of flow of the refrigerant. When the compressor 100 is in operation, the refrigerant circulates along the circulation line 12 according to the discharge capacity of the compressor 100. That is, the compressor 100 performs a sequence of processes including a step of sucking the refrigerant, a step of compressing the sucked refrigerant, and a step of discharging the compressed refrigerant.

The evaporator 18 also constitutes a part of an air circuit of the vehicular air-conditioning system, and air passing through the evaporator 18 is cooled by the refrigerant taking heat to evaporate within the evaporator 18. The compressor 100 to which a capacity control system A is applied is a variable capacity compressor, for example, a swash plate clutchless compressor. The compressor 100 includes a cylinder block 101, and the cylinder block 101 has a plurality of cylinder bores 101 a. A front housing 102 is connected to an end of the cylinder block 101, and a rear housing (cylinder head) 104 is connected to the other end of the cylinder block 101 via a valve plate 103.

The cylinder block 101 and the front housing 102 define a crank chamber 105, and a drive shaft 106 extends axially inside the crank chamber 105. The drive shaft 106 extends through an annular swash plate 107 placed inside the crank chamber 105, and the swash plate 107 is hinged to a rotor 108 fixed on the drive shaft 106, by a joint 109. The swash plate 107 can therefore tilt while moving along the drive shaft 106.

A coil spring 110 is mounted on the drive shaft 106, between the rotor 108 and the swash plate 107, to push the swash plate 107 to tilt at a minimum angle. On the opposite side of the swash plate 107, specifically between the swash plate 107 and the cylinder block 101, a coil spring 111 is mounted on the drive shaft 106 to push the swash plate 107 to tilt at a maximum angle. The drive shaft 106 extends through a boss 102 a projecting outward from the front housing 102, and a pulley 112 as a power transmission device is connected to the outer end of the drive shaft 106. The pulley 112 is rotatably mounted on the boss 102 a by means of a ball bearing 113, and a belt 115 is put around the pulley of an engine 114 as an external drive source.

An axis sealing device 116 is disposed inside the boss 102 a to shield the inside of the front housing 102 from the outside thereof. The drive shaft 106 is rotatably supported by bearings 117, 118, 119, 120 in its radial and thrust directions. When from the engine 114 is power transmitted to the pulley 112, the drive shaft 106 can rotate in synchronization with the rotation of the pulley 112.

A piston 130 is fitted within the cylinder bore 101 a. The piston 130 has a tail portion integrally projecting into the crank chamber (control pressure chamber) 105. In a recess 130 a in the tail portion, a pair of shoes 132 is provided. The shoes 132 are in sliding contact with the periphery of the swash plate 107 on both sides thereof. Thus, the shoes 132 enable the piston 130 and the swash plate 107 to move in association with each other. The rotation of the drive shaft 106 causes the piston 130 to reciprocate in the cylinder bore 101 a.

The rear housing 104 defines a suction chamber (suction pressure area) 14.0 and a discharge chamber (discharge pressure area) 142. The suction chamber 140 can communicate with each cylinder bore 101 a via each suction hole 103 a in the valve plate 103. The discharge chamber 142 communicate with each cylinder bore 101 a via each discharger hole 103 b in the valve plate 103. The suction hole 103 a and the discharge hole 103 b are opened and closed by an suction valve and a discharge valve, not shown, respectively.

A muffler 150 is provided outside the cylinder block 101. A muffler base 101 b is formed integral with the cylinder block 101, and a muffler casing 152 is connected to the muffler base 101 b with an unillustrated sealing member. The muffler casing 152 and the muffler base 101 b define a muffler space 154, and the muffler space 154 is connected to the discharge chamber 142 by a discharge passage 156 which penetrates the rear housing 104, the valve plate 103 and the muffler base 101 b.

The muffler casing 152 has a discharge port 152 a, and a check valve 200 is provided in the muffler space 154 to prevent flow between the discharge passage 156 and the discharge port 152 a. Specifically, the check valve 200 opens or closes depending on a difference in pressure between the discharge passage 156 and the muffler space 154; the check valve 200 closes when the pressure difference becomes smaller than a predetermined value, and opens when the pressure difference becomes greater than the predetermined value.

Thus, the discharge chamber 142 can become connected to the outgoing side of the circulation line 12 via the discharge passage 156, the muffler space 154 and the discharge port 152 a, and the muffler space 154 is connected or disconnected by the check valve 200. The suction chamber 140 is connected to the return passage of the circulation line 12 via a suction port 104 a in the rear housing 104.

The rear housing 104 accommodates a capacity control valve (electromagnetic valve) 300, which is interposed in a gas supply passage 160. The gas supply passage 160 extends from the rear housing 104 to the cylinder block 101 through the valve plate 103, thereby connecting the discharge chamber 142 and the crank chamber 105.

The suction chamber 140 is connected to the crank chamber 105 by an extraction passage 162. The extraction passage 162 is comprised of a clearance between the drive shaft 106 and the bearing 119, 120, a space 164 and a fixed orifice 103 c in the valve plate 103. The suction chamber 140 is connected to the capacity control valve 300, independently from the gas supply passage 160, by a pressure sensing passage 166 formed in the rear housing 104. More specifically, as shown in FIG. 2, the capacity control valve 300 includes a valve unit 300A and a solenoid unit 300B which opens and closes the valve unit 300A. The valve unit 300A has an approximately cylindrical valve housing 301, with a valve hole 301 a formed in substantially the center of the valve housing 301. The valve hole 301 a extends in the axial direction of the valve housing 301, and one end of the valve hole 301 a is connected to a first pressure sensing chamber 302 defined in the valve housing 301.

A communication hole 301 b is formed in the portion of the valve housing 301 which forms the peripheral wall of the first pressure sensing chamber 302. The communication hole 301 b communicates with the discharge chamber 142 via the upstream portion of the gas supply passage 160. Therefore, the valve hole 301 a communicates with the discharge chamber 142 via the first pressure sensing chamber 302, the communication hole 301 b and the upstream portion of the gas supply passage 160.

The other end of the valve hole 301 a is connected to a valve chamber 303 defined inside the valve housing 301. The valve chamber 303 has an outlet port 301 c formed therein, which penetrates the valve housing 301 in the radial direction. Therefore, the valve chamber 303 communicates with the crank chamber 105 via the outlet port 301 c and the downstream portion of the gas supply passage 160.

One end of an insertion hole 304 is connected to the valve chamber 303 on the opposite side to the valve hole 301 a. Like the valve hole 301 a, the insertion hole 304 extends along the axis of the valve housing 301. The other end of the insertion hole 304 is connected to a second pressure sensing chamber 305 in which a pressure sensing port 301 d penetrating the valve housing 301 in the radial direction is connected. Therefore, the second pressure sensing chamber 305 communicates with the suction chamber 140 via the pressure sensing port 301 d and the pressure sensing passage 166.

A cylindrical valve body 306 is disposed in the valve housing 301. As shown in enlargement in FIG. 3, one end of a cylindrical slide part 307 is continual to the back of the valve body 306 integrally and coaxially, and the slide part 307 is slidably supported by the insertion hole 304.

One end of a shaft part 308 is continual to the opposite side of the slide part 307 integrally and coaxially, and the shaft part 308 is positioned in the second pressure sensing chamber 305. A hemispherical head portion 309 with a larger diameter than the shaft part 308 is formed integral with the opposite side of the shaft part 308. A release spring 310 comprised of a conical coil spring is disposed between the end wall of the second pressure sensing chamber 305 where the insertion hole 304 is connected and the head portion 309, and urges the valve body 306 in the direction away from the valve hole 301 a (valve opening direction).

The proximal end of a transmission rod 311 is connected to the front side of the valve body 306 coaxially and integrally. The transmission rod 311 penetrates the valve hole 301 a. The outside diameter of the transmission rod 311 is smaller than the inside diameter of the valve hole 301 a, and the distal end of the transmission rod 311 reaches inside the first pressure sensing chamber 302.

Referring to FIG. 2 again, the solenoid unit 300B has an approximately cylindrical solenoid housing 320 which is coaxially connected to the other end of the valve housing 301 by press fitting. An open end of the solenoid housing 320 is closed with an end cap 322. A cylindrical coil (solenoid coil) 326 covered with a resin member 324, is accommodated in the solenoid housing 320.

Also an approximately cylindrical fixed core 328 is concentrically accommodated in the solenoid housing 320. The fixed core 328 extends from the valve housing 301 toward the end cap 322, up to the middle of the coil 326. The end cap 322 side of the fixed core 328 is surrounded by a cylindrical member 330, which has a closed end on the end cap 322 side. A support member 332 is disposed in close contact with the closed end of the cylindrical member 330 inside the cylindrical member 330. A movable core retaining space 335 which retains an approximately cylindrical movable core 334 is defined between the fixed core 318 and the support member 332.

The fixed core 328 has a center hole 328 a whose one end is connected to the movable core retaining space 335. A solenoid rod 336 is inserted in the center hole 328 a, and protrudes from both ends of the fixed core 328. The movable core 334 is integrally fixed at the portion of the solenoid rod 336 which laterally crosses the movable core retaining space 335. The solenoid rod 336 reaches the support member 332, and the support member 332 side end of the solenoid rod 336 is slidably supported by a cylindrical bottomed hole of the support member 332.

The movable core 334, the fixed core 328, the solenoid housing 320 and the end cap 322 are formed of a magnetic material, and form a magnetic circuit. The cylindrical member 330 is formed of a stainless material which is a non-magnetic material.

A compression coil spring 338 is disposed between the movable core 334 and the support member 332 to urge the movable core 334 in a direction away from the support member 332 (valve closing direction).

It is to be noted that a predetermined clearance is secured between the movable core 324 and the fixed core 328. The outside diameter of the movable core 334 is smaller than the inside diameter of the cylindrical member 330, with a clearance secured between the movable core 334 and the cylindrical member 330.

Referring to FIG. 3 again, the other end of the center hole 328 a is connected to the second pressure sensing chamber 305, and the inside diameter of the center hole 328 a is reduced at the protruding end of the fixed core 328 protruding inside the second pressure sensing chamber 305. The second pressure sensing chamber 305 side end of the solenoid rod 336 is slidably supported by the protruding end of the fixed core 328, i.e., the diameter-reduced portion of the center hole 328 a. The end of the solenoid rod 336 protruding into the second pressure sensing chamber 305 abuts on the head portion 309.

A communication hole 339 is formed in the base of the protruding end of the fixed core 328, and the second pressure sensing chamber 305 communicates with the movable core retaining space 335 via the communication hole 339 and the center hole 328 a. Therefore, the entire solenoid rod 336 is exposed to the pressure of the suction chamber 140 or the suction pressure Ps, so that the suction pressure Ps acts on the valve body 306 in the valve closing direction in the region that is defined by the cross section of the slide part 307 which defines the second pressure sensing chamber 305 and the valve chamber 303.

A control device 400 provided outside the compressor 100 is connected to the coil 326 (see FIG. 2). When the control current I is supplied to the coil 326 from the control device 400, the solenoid unit 300B generates the electromagnetic force F(I). The electromagnetic force F(I) of the solenoid unit 300B pulls the movable core 334 toward the fixed core 328, and acts on the valve body 306 in the valve closing direction via the solenoid rod 336.

As shown in enlargement in FIG. 4, the pressure sensitive unit 340 is disposed in the first pressure sensing chamber 302, and has a disk-like base 341. The base 341 is press fitted in an opening end of the peripheral wall of the valve housing 301 to be fitted airtightly.

A cylindrical stopper 342 integrally protrudes from the center of the inner surface of the base 341, and a bellows 343 is disposed around the stopper 342. One end of the bellows 343 is airtightly secured to the base 341, and the other end of the bellows 343 is airtightly secured to a cap 344. The interior of the bellows 343 is kept vacuum (pressure-reduced state).

The cap 344 includes a cylindrical part 344 a, a flange 344 b continual to one end of the cylindrical part 344 a, and an end wall part 344 c which closes the other end of the cylindrical part 344 a. A compression coil spring 345 is disposed between the base 341 and the flange 344 b of the cap 344, and surrounds the bellows 343.

The compression coil spring 345 and the bellows 343 are expandable and contractible in the axial direction of the valve housing 301, i.e., in the valve opening direction or the valve closing direction. Therefore, the pressure sensitive unit 340 displaces in the valve opening direction or the valve closing direction according to the pressure of the first pressure sensing chamber 302 (pressure of the discharge pressure area), but the expansion/contraction amount of the pressure sensitive unit 340 is limited. The contraction of the pressure sensitive unit 340 is restricted by the abutment of the end wall part 344 c of the cap 344 on the stopper 342.

The cylindrical part 344 a and the end wall part 344 c of the cap 344 form a recess recessed toward the stopper 342 from the end surface of the pressure sensitive unit 340, and the distal end of the transmission rod 311 reaches the interior of the recess of the cap 344 of the pressure sensitive unit 340. The end wall part 344 c of the cap 344 can move closer to or away from the distal end of the transmission rod 311 according to the expansion/contraction amount of the pressure sensitive unit 340.

FIG. 4 shows the state where the pressure sensitive unit 340 is expanded so that the distal end of the transmission rod 311 abuts on the end wall part 344 c of the cap 344. In this state, the pressure sensitive unit 340 and the valve body 306 are connected to each other via the transmission rod 311.

FIG. 5 shows the state where the pressure sensitive unit 340 is contracted compared with FIG. 4 so that the distal end of the transmission rod 311 is separated from the end wall part 344 c of the cap 344. In this state, the pressure sensitive unit 340 and the valve body 306 are separated from each other. The distal end of the transmission rod 311 does not come off from the recess of the cap 344 even when the pressure sensitive unit 340 contracts most. The recess of the cap 344 serves as a guide when the end wall part 344 c of the cap 344 moves closer to or away from the distal end of the transmission rod 311.

Therefore, as the pressure of the discharge chamber 142, i.e., the discharge pressure area (hereinafter referred to as “discharge pressure Pd”) drops, the pressure sensitive unit 340 expands and the cap 344 of the pressure sensitive unit 340 moves toward the valve body 306. When the pressure sensitive unit 340 tends to expand further after the end wall part 344 c of the cap 344 abuts on the distal end of the transmission rod 311, the valve body 306 is pushed in the valve opening direction via the transmission rod 311.

The amount of press fitting of the base 341 of the pressure sensitive unit 340 into the valve housing 301 is adjusted in such a way that the capacity control valve 300 performs the desired operation.

The following are the forces acting on the valve body 306 of the capacity control valve 300 in different cases.

Case A: where the pressure sensitive unit 340 contracts to be separated from the distal end of the transmission rod 311

In this case, the pressing force from the pressure sensitive unit 340 does not act on the valve body 306. The discharge pressure Pd, the pressure of the crank chamber 105 (crank pressure Pc), the pressure of the suction chamber 140, i.e., the suction pressure area (suction pressure Ps), urging force fs1 of the release spring 310, and electromagnetic force F(I) of solenoid unit 300B act on the valve body 306.

Given that Sv is the pressure receiving area (first pressure receiving area) of the valve body 306 on which the discharge pressure Pd acts in the valve opening direction through the first pressure sensing chamber 305 and the valve hole 301 a, and Sr is the pressure receiving area (second pressure receiving area) of the valve body 306 which is defined by the cross-sectional area of the slide part 307 and on which the suction pressure Ps in the second pressure sensing chamber 305 acts in the valve closing direction, the first pressure receiving area Sv is preferably set slightly larger than the second pressure receiving area Sr. Accordingly, the crank pressure Pc acts on the valve body 306 at the area of (Sv−Sr) slightly in the valve closing direction. As a result, excessive opening of the valve body 306 is restrained, stabilizing the opening/closing operation of the valve body 306.

Therefore, the discharge pressure Pd acts on the valve body 306 in the valve opening direction, and the suction pressure Ps and the crank pressure Pc act thereon in the valve closing direction opposite to the valve opening direction.

In the case A, the force acting on the valve body 306 can be expressed by the following equation (1), and transforming the equation (1) with Pc=Ps+α yields equation (2). It is empirically known that Pc=Ps+α, i.e., when the difference α between the crank pressure Pc and the suction pressure Ps lies within an approximately certain range. Transforming the equation (2) to have Pd−Ps on the left-hand term yields equation (3). If the solenoid unit 300B is designed so that the electromagnetic force F(I) is proportional to the control current I, transforming the equation (3) with F(I)=AI (A is a coefficient) yields equation (4).

Sv>Sr and fs1>fs2.

Eq. 1

Pd·Sv−Ps·Sr−Pc·(Sv−Sr)+fs1−fs2−F(I)=0  (1)

(Pd−Ps)·Sv−α·(Sv−Sr)+fs1−fs2−F(I)=0  (2)

Pd−Ps=1/Sv·F(I)+(Sv−Sr)/Sv·α−(fs1−fs2)/Sv  (3)

Pd−Ps=A/Sv·I+(Sv−Sr)/Sv·α−(fs1−fs2)/Sv  (4)

The equation (3) shows that the differential pressure (Pd−Ps differential pressure) between the discharge pressure Pd and the suction pressure Ps can be regulated with the electromagnetic force F(I) generated in the solenoid unit 300B, i.e., the current (control current) I supplied to the coil 326 of the solenoid unit 300B. The electromagnetic force F(I) is proportional to the control current I, and acts on the valve body 306 in the valve closing direction. As shown in FIG. 6, therefore, as the control current I is increased, the Pd−Ps differential pressure increases. That is, the Pd−Ps differential pressure can be set to an arbitrary value by regulating the control current I.

The control device 400 sets the target value of the control current I based on the external information detected by the external information detecting means. As the control current I with the target value is supplied to the coil 326, the degree of the valve opening of the capacity control valve 300 is adjusted so that the Pd−Ps differential pressure approaches the target differential pressure ΔPset. In other words, the Pd−Ps differential pressure is controlled through feedback control in the case A.

Since the urging force fs1 of the release spring 310 is set greater than the urging force fs2 of the compression coil spring 338, the valve body 306 opens the valve hole 301 a with the urging force of the release spring 310 given that the control current I is set to zero. As a result, the refrigerant (discharge gas) in the discharge chamber 142 is supplied into the crank chamber 105, and the discharge capacity is kept minimum.

Case B: where the pressure sensitive unit 340 expands and abuts on the distal end of the transmission rod 311

In this case, the pressing force from the pressure sensitive unit 340 acts on the valve body 306 in the valve opening direction. As shown by the following equation (5), therefore, the force acting on the valve body 306 is (fs3−Pd·Sb) as the pressing force from the pressure sensitive unit 340 added to the left-hand term of the equation (1). fs3 is the urging force of the compression coil spring 345, and Sb is the effective area of the bellows 343 or the pressure receiving area (third pressure receiving area) at which the discharge pressure Pd acts on the pressure sensitive unit 340 in the contraction direction.

Transforming the equation (5) with Pc=Ps+α and Sv=Sb yields equation (6). Transforming the equation (6) to have Ps on the left-hand term yields equation (7). Transforming the equation (7) with F(I)=A·I (A is a coefficient) yields equation (8).

Eq. 2

fs3−Pd·Sb+Pd·Sv−Ps·Sr−Pc·(Sv−Sr)+fs1−fs2−F(I)=0  (5)

−Ps·Sv−α·(Sv−Sr)+fs1−fs2+fs3−F(I)=0  (6)

Ps=−1/Sv·F(I)−(Sv−Sr)/Sv·α+(fs1−fs2+fs3)/Sv  (7)

Ps=−A/Sv·I−(Sv−Sr)/Sv·α−(fs1−fs2+fs3)/Sv  (8)

In the case B where the pressure sensitive unit 340 abuts on the distal end of the transmission rod 311, the direction in which the discharge pressure Pd directly acts on the valve body 306 and the direction in which the discharge pressure Pd acts on the bellows 343 are opposite to each other. In addition, the first pressure receiving area Sv and the third pressure receiving area Sb are set substantially equal to each other (Sv=Sb), the discharge pressures Pd in the opposite directions (opposing directions) cancel out each other, so that the influence of the discharge pressure Pd on the valve body 306 is substantially eliminated. The case where the first pressure receiving area Sv and the third pressure receiving area Sb are substantially equal to each other include a case where there is a difference between the first pressure receiving area Sv and the third pressure receiving area Sb which can be regarded approximately identical from the view of the designed target (e.g., including a case where there is a difference which is produced by productional variations in the dimensions of parts which define the first pressure receiving area Sv and the third pressure receiving area Sb) as well as the case where the first pressure receiving area Sv and the third pressure receiving area Sb are identical.

Therefore, the equation (8) shows that the suction pressure Ps can be regulated with the electromagnetic force F(I) generated in the solenoid unit 300B, i.e., the control current I. When the control current I is increased, the electromagnetic force F(I) acts on the valve body 306 in the valve closing direction. Therefore, the suction pressure Ps can be reduced as the current I is increased as shown in FIG. 7. The control device 400 sets a target suction pressure Pss which is the target value of the suction pressure Ps based on the external information from the external information detecting means. Setting the target suction pressure Pss is equivalent to setting the target value of the control current I. As the control current I with the target value is supplied to the coil 326 of the solenoid unit 300B, the degree of the valve opening of the capacity control valve 300 is adjusted so that the suction pressure Ps approaches the target suction pressure Pss.

In other words, the capacity control system A controls the discharge capacity by the differential pressure control method which performs feedback control of the Pd−Ps differential pressure in the case A where the pressure sensitive unit 340 contacts to be separated from the distal end of the transmission rod 311. In the case B where the pressure sensitive unit 340 expands to abut on the distal end of the transmission rod 311, on the other hand, the capacity control system A controls the discharge capacity by the suction pressure control method which performs feedback control of the suction pressure Ps.

Note that the state where the urging force fs3 of the compression coil spring 345 of the pressure sensitive unit 340 is balanced with the discharge pressure Pd acting on the pressure sensitive unit 340 is expressed by the equation fs3−Pd·Sb=0. The pressure sensitive unit 340 is disposed in such a way that when the pressure sensitive unit 340 is in the balanced state and the valve body 306 is positioned at the valve closing position of closing the valve hole 301 a, the pressure sensitive unit 340 simply contacts the distal end of the transmission rod 311, and does not abut thereon.

Given that the discharge pressure Pd in the balanced state is a set pressure Pds of the pressure sensitive unit 340, Pds=fs3/Sb. In consideration of the set pressure Pds, the expansion/contraction of the pressure sensitive unit 340 from the balanced state and the contact/separation of the pressure sensitive unit 340 with/from the distal end of the transmission rod 311 are determined by the following conditions.

When the discharge pressure Pd is greater than the set pressure Pds (Pd>Pds), the pressure sensitive unit 340 contracts to be separated from the distal end of the transmission rod 311. That is, the pressure sensitive unit 340 and the valve body 306 are separated.

When the discharge pressure Pd is equal to or less than the set pressure Pds (Pd≦Pds), the pressure sensitive unit 340 expands to abut on the distal end of the transmission rod 311. That is, the pressure sensitive unit 340 and the valve body 306 are connected together.

When the discharge pressure Pd becomes equal to or lower than the set pressure Pds, therefore, the capacity control system A adopts the suction pressure control method via the capacity control valve 300. Accordingly, even when the cooling load is small, the discharge capacity is controlled stably, and the risk of damaging the compressor 100 is reduced even when the amount of the refrigerant is insufficient.

FIG. 8 is a block diagram showing the schematic configuration of the capacity control system A including the control device 400. The capacity control system A has external information detecting means which detects one or more pieces of external information, and includes evaporator target outlet air temperature setting means 401 and an evaporator temperature sensor 402.

The evaporator target outlet air temperature setting means 401 sets an evaporator target outlet air temperature Tes based on the various kinds of external information including cabin temperature setting. The evaporator target outlet air temperature Tes is the last target in the discharge capacity control of the compressor 100, and the target value of an air temperature Te at the outlet of the evaporator 18. The evaporator target outlet air temperature setting means 401 inputs the set evaporator target outlet air temperature Tes as one piece of external information to the control device 400. The evaporator target outlet air temperature setting means 401 can be constructed by, for example, a part of an air-conditioning ECU which controls the general operation of the air-conditioning system. That is, the evaporator target outlet air temperature setting means 401 may set the target value for the control amount of the vehicle air-conditioning system.

The evaporator temperature sensor 402 is disposed at the outlet of the evaporator 18 in the air circuit to detect the air temperature Te which has just passed the evaporator 18 (see FIG. 1). The detected air temperature Te is input to the control device 400 as one piece of external information.

Further, the external information detecting means includes discharge pressure detecting means, which has a pressure sensor 403 constituting a part thereof. The discharge pressure detecting means detects the discharge pressure Pd. The pressure sensor 403 is mounted to, for example, the inlet side of the radiator 14 to detect the pressure of the refrigerant at this portion, and inputs the pressure to the control device 400 (see FIG. 1). When there is a pressure difference between the mount portion of the pressure sensor 403 and the discharge chamber 142, the discharge pressure Pd can be detected after the detected pressure from the pressure sensor 403 is corrected by the pressure difference.

The control device 400 has control target setting means 410 and current regulating means 411.

The control target setting means 410 sets the target of the control current I as a control target based on a difference ΔT between the evaporator outlet air temperature Te actually detected by the evaporator temperature sensor 402 and evaporator target outlet air temperature Tes set by the evaporator target outlet air temperature setting means 401. Specifically, the target of the control current I is set under PI control or PID control based on the difference ΔT.

When the discharge pressure Pd is greater than the set pressure Pds of the pressure sensitive unit 340, the pressure sensitive unit 340 of the capacity control valve 300 is separated from the transmission rod 311, so that the setting of the target of the control current I is to set a target differential pressure ΔPset as the target of Pd−Ps differential pressure.

In this case, for example, the target differential pressure ΔPset is set within the range between an upper limit ΔPmax and a lower limit ΔPmin of a preset target differential pressure ΔP, as shown in FIG. 6. Then, the target of the control current I is set based on the target differential pressure ΔPset.

The target of the control current I is set within the range between a lower limit IL1 and an upper limit IH1 which are preset.

When the discharge pressure Pd is equal to or slightly lower than the set pressure Pds of the pressure sensitive unit 340, the pressure sensitive unit 340 of the capacity control valve 300 abuts on the transmission rod 311, so that the setting of the target of the control current I is to set the target suction pressure Pss as the target of the suction pressure Ps.

For example, when the discharge pressure Pd detected by the discharge pressure detecting means is equal to or slightly lower than the set pressure Pds of the pressure sensitive unit 340, as shown in FIG. 7, the target of the control current I is set within the range between a lower limit IL2 and an upper limit IH2 of the control current I which respectively correspond to a preset upper limit PssH and a preset lower limit PssL of the target suction pressure Pss.

The upper limit PssH can be set to a value lower than the set pressure Pds (=fs3/Sb) of the pressure sensitive unit 340 by a predetermined value, and the lower limit PssL can be set from the viewpoint of the air-conditioning performance and protection in case of deficient refrigerant.

The current regulating means 411 supplies the control current I to the coil 326 based on the target of the control current I set by the control target setting means 410 to drive the capacity control valve 300.

FIG. 9 exemplifies the schematic configuration of the current regulating means 411. The current regulating means 411 has a switching element 420 which is interposed in a power line extending between a power source 430 and the ground in series to the coil 326 of the capacity control valve 300. The switching element 420 can disconnect the power line, and the operation of the switching element 420 allows the control current I to be supplied to the coil 326 in PWM (Pulse Width Modulation) at a predetermined drive frequency (e.g., 400 to 500 Hz). To form a flywheel circuit, a diode 421 is connected in parallel to the coil 326.

A predetermined drive signal is input to the switching element 420 from control signal generating means 422 to change the duty ratio in PWM according to the signal. A current sensor 423 is interposed in the power line to detect the control current I flowing in the coil 326. The set location of the current sensor 423 is not particularly limited as long as the current sensor 423 can detect the control current I, and the sensor is not limited to an ammeter and may be a voltmeter if it can detect a physical quantity equivalent to the control current I.

The current sensor 423 inputs the detected control current I to control current comparing/determining means 424 which compares the target of the control current I set by the control target setting means 410 with the control current I detected by the current sensor 423. Based on the comparison result, the control current comparing/determining means 424 changes the drive signal generated by the control signal generating means 422 in such a way that the detected control current I approaches the target of the control current I.

The invention is not limited to the foregoing embodiment, and may be modified in various forms.

For example, the capacity control valve may take the following modifications.

While the pressure sensitive unit 340 has the compression coil spring 345 disposed around the bellows 343, a pressure sensitive unit which has the compression coil spring disposed inside the bellows may be used.

The transmission rod may be formed by a separate component from the valve body.

A pressure sensitive unit which uses a diaphragm in place of the bellows 343 may be used.

The first pressure receiving area Sv of the valve body 306 and the pressure receiving area of the pressure sensitive unit 340, namely the effective area Sb of the bellows 343, may not be set substantially identical, but may be set like Sb>Sv or Sb<Sv, so that the discharge pressure Pd is intentionally permitted to act on the valve body 306.

Although the urging force fs1 of the release spring 310 is set larger than the urging force fs2 of the compression coil spring 338 (fs1>fs2), it may be set to fs1<fs2.

Although the set pressure Pds of the pressure sensitive unit 340 is assumed to be a comparatively low value within the range in which the discharge pressure Pd is variable in the first embodiment, the urging force of the compression coil spring 345 may be set large to set the set pressure Pds high. Setting the set pressure Pds high can widen the control range in the suction pressure control method. The set pressure Pds can be set properly according to the design conditions.

The variable capacity compressor can take, for example, the following modifications.

While the compressor 100 in the first embodiment is a swash plate clutchless compressor, a compressor having a clutch mechanism may be used. The compressor is not limited to a swash plate type, and a variable capacity compressor of a wobble-plate type, a scroll type, a vane type or the like may be used if it can regulate the pressure of the control pressure chamber to control the discharge capacity. Further, a compressor which is driven with an electric motor may be used.

The refrigerant which is used in the refrigeration cycle 10 is not particularly limited.

The capacity control system can take, for example, the following modifications.

When the discharge pressure Pd is greater than the set pressure Pds of the pressure sensitive unit 340, the capacity control valve 300 and the pressure sensitive unit 340 are separated from each other, so that the control target setting means 410 sets the target differential pressure ΔPset which is the target for the Pd−Ps differential pressure as the target of the control current I. However, the control target setting means 410 may set a physical quantity target other than the Pd−Ps differential pressure as the control target value.

For example, when the capacity control valve 300 and the pressure sensitive unit 340 are separated from each other, the control target setting means 410 may set the target suction pressure Pss which is the target value of the suction pressure Ps, and regulate the control current I so that the suction pressure Ps approaches the target suction pressure Pss.

Specifically, transforming the aforementioned equation (4) yields the following equation (9). Although the right-hand side of the equation (9) includes a term containing the discharge pressure Pd, the discharge pressure Pd can be detected by the pressure sensor 403. Therefore, referring to FIG. 10, the equation (9) shows that the suction pressure Ps can be controlled if the discharge pressure Pd can be detected. Transforming the equation (9) and substituting the target suction pressure Pss for the suction pressure Ps yields equation (10) where Sy>Sr and fs1>fs2.

Eq. 3

Ps=−A/Sv·I+Pd−(Sv−Sr)/Sv·α+(fs1−fs2)/Sv  (9)

I=A/Sv·(Pd−Pss)−(Sv−Sr)/Sv·α−(fs1−fs2)/Sv  (10)

In this case, the control target setting means 410 can set the target suction pressure Pss as the control target based on the difference ΔT between the evaporator outlet air temperature Te actually detected by the evaporator temperature sensor 402 and the evaporator target outlet air temperature Tes set by the evaporator target outlet air temperature setting means 401. The control target setting means 410 may calculate the target of the control current I from the target suction pressure Pss and the discharge pressure Pd detected by the pressure sensor 403 using the equation (10), and the current regulating means 411 may supply the control current I to the coil 326 so that the control current I approaches the target of the control current I. Even with the target suction pressure Pss set constant, if the discharge pressure Pd varies, the target of the control current I varies based on the equation (10) in which case the control current I is not the control target value.

According to this method, even when the pressure sensitive unit 340 is set apart from the transmission rod 311, the suction pressure Ps can be controlled as the control target. Therefore, the suction pressure Ps can be controlled regardless of whether the discharge pressure Pd is high or low. Since this method controls the suction pressure Ps without substantially using the pressure sensitive unit 340, the control range of the suction pressure Ps is wider than that in the related art.

INDUSTRIAL APPLICABILITY

The present invention can be used as a capacity control valve, a variable capacity compressor, and a capacity control system, which control a discharge capacity stably even when the cooling load is small, and reduce the risk of damaging the compressor even when the quantity of the refrigerant is insufficient. 

1. A capacity control valve, disposed in a communication passage communicating a discharge pressure area with a control pressure chamber in a variable capacity compressor, for regulating a pressure in the control pressure chamber to control a discharge capacity of the variable capacity compressor, the capacity control valve comprising: a solenoid unit; a valve body on which a pressure of the discharge pressure area of the variable capacity compressor acts in a valve opening direction, and a pressure of a suction pressure area of the variable capacity compressor and an electromagnetic force of the solenoid unit acts in a valve closing direction opposite to the valve opening direction; and a pressure sensitive unit on which the pressure of the discharge chamber acts, and which is connected to the valve body to apply urging force in the valve opening direction on the valve body according to the pressure of the discharge pressure area when the pressure of the discharge pressure area is lower than a set pressure, and is separated from the valve body when the pressure of the discharge pressure area is higher than the set pressure.
 2. The capacity control valve according to claim 1, wherein a first pressure receiving area of the valve body on which the pressure of the discharge pressure area acts is equal to or greater than a second pressure receiving area of the valve body on which the pressure of the suction pressure area of the variable capacity compressor acts.
 3. The capacity control valve according to claim 2, wherein the pressure sensitive unit is disposed in such a way that the pressure of the discharge pressure area acts on the pressure sensitive unit and the valve body in opposite directions.
 4. The capacity control valve according to claim 3, wherein the first pressure receiving area is set, in the pressure sensitive unit, substantially identical to a third pressure receiving area on which the pressure of the discharge pressure area acts.
 5. The capacity control valve according to claim 1, wherein the pressure sensitive unit is disposed, in the communication passage, in an area extending between the discharge pressure area and a valve hole of the capacity control valve.
 6. A variable capacity compressor comprising: a housing having a discharge chamber as the discharge pressure area, a crank chamber as the control pressure chamber, a suction chamber, and a cylinder bore defined therein; a piston placed in the cylinder bore; a drive shaft rotatably supported in the housing; a conversion mechanism including a swash plate element of a variable tilt angle which converts rotation of the drive shaft to a reciprocal motion of the piston; and the capacity control valve as set forth in claim
 1. 7. A capacity control system for a variable capacity compressor, comprising the capacity control valve as set forth in claim 1, external information detecting means which detects external information, control target setting means which sets a control target value based on the external information detected by the external information detecting means, and current regulating means which regulates a current to be supplied to the solenoid unit based on the control target value set by the control target setting means, and controlling a discharge capacity of the variable capacity compressor by regulating the pressure of the control pressure chamber, the external information detecting means including discharge pressure detecting means for detecting the pressure of the discharge pressure area, wherein when the pressure of the discharge pressure area detected by the discharge pressure detecting means is lower than the set pressure, the control target setting means sets a target suction pressure which is a target value of the pressure of the suction pressure area as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit based on the target suction pressure.
 8. The capacity control system for a variable capacity compressor according to claim 7, wherein when the pressure of the discharge pressure area detected by the discharge pressure detecting means is higher than the set pressure, the control target setting means sets the target suction pressure which is the target value of the pressure of the suction pressure area as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit based on the pressure of the discharge pressure area detected by the discharge pressure detecting means, and the target suction pressure.
 9. The capacity control system for a variable capacity compressor according to claim 7, wherein when the pressure of the discharge pressure area detected by the discharge pressure detecting means is higher than the set pressure, the control target setting means sets a target value for the current to be supplied to the solenoid unit as the control target value, and the current regulating means regulates the current to be supplied to the solenoid unit in such a way as to approach the target value of the current. 